Two-stroke internal combustion engines



y 1961 c. A. WOOD-COLLINS 2,985,158

TWO-STROKE INTERNAL COMBUSTION ENGINES Filed March 24. 1959 INVENTOR CHARLES A. WOOD-COLLINS ATTORNEYS United States Patent 9 TWO-STROKE INTERNAL COMBUSTION ENGINES Charles A. Wood-Collins, London, England, assignor to D. Napier & Son Limited, London, England, a company of Great Britain Filed Mar. 24, 1959, Ser. No. 801,547

Claims priority, application Great Britain Mar. 25, 1958 1 Claim. (Cl. 12365) This invention relates to two-stroke internal combustion engines of either the compression ignition fuel injection type or the carburetted or fuel injection type with spark ignition.

For certain application, for example in rail traction systems incorporating mechanical transmission, it is important that the output torque from the engine at low speeds should be maintained at a relatively high value or even be increased above the torque at full speeds. One common method of achieving such a torque characteristic is to provide the engine with one or more compressors arranged to supply supercharging and scavenge air to the engine cylinders, these compressors being driven independently of the engine so that the pressure of air delivered to the cylinders can be maintained or even increased at low engine speeds.

It is an object of the present invention to provide an alternative system for maintaining the required torque characteristics in a simple and eflective manner, and according to the present invention a two-stroke engine includes an adjustable throttle valve in the exhaust manifold and a positive displacement blower arranged to deliver compressed air to the cylinder or cylinders of the engine.

The valve may be manually controlled, but is preferably automatically controlled by a device sensitive to a variable operating condition of the engine which alters with the speed of the engine.

Thus the device may be sensitive to air pressure at some point in the system, but preferably it is directly sensitive to the speed of rotation of the engine.

According to a preferred feature of the invention the device is arranged to close the throttle valve progressively as the speed of the engine falls.

Conveniently the blower is driven from the engine crankshaft.

It will be appreciated that since the positive displacement blower is essentially a constant volume machine the presence of a restriction in the exhaust duct will cause the air pressure and density in the cylinder to increase and so improve the output torque. Other thingsbeing equal the engine output torque is a substantially direct function of air density in the engine cylinder or cylinders.

The throttle valve may be manipulated in accordance with speed variations to provide any desired engine torque characteristics to suit special requirements. In particular it is possible by control of the throttle valve to provide a torque characteristic which rises progressively as engine speed falls.

The throttle valve may be manually or automatically controlled and where the automatic control is provided this is preferably effected by means of a device sensitive to an operating condition of the engine which varies with engine speed. For example the device may be sensitive to the pressure in the exhaust duct itself, but preferably the device comprises a speed responsive governor connected directly to the engine crankshaft and arranged to actuate the throttle valve through a servo mechanism "ice including linkages or cams arranged to give the required torque characteristic.

The invention may be performed in various different ways but one specific embodiment will now be described by way of example with reference to the accompanying drawing which shows diagrammatically an exhaust throttle valve and automatic control system in accordance with the invention.

In this example a reciprocating two-stroke compression ignition internal combustion engine 10 is provided with a positive displacement supercharging and scaveng ing compressor 11 which may be of the well known type embodying two helical rotors rotating in opposite directions, the compressor being mechanically coupled to and driven by an extension 12 of the crankshaft of the engine. The compressor supplies supercharging and scavenging air to the engine via an air intake 13. The exhaust gases from the engine are discharged through an exhaust duct 14 which contains a butterfly exhaust throttle valve 15. Fuel is injected into the engine cylinders in well known manner by a series of fuel injector pumps incorporated into a pump control unit 16 having a control member 17 which serves to adjust the quantity of fuel injected per cycle of the engine, this member 17 being under the control of a lever 8 which may be manually operated or under governor control.

The exhaust throttle valve 15 is controlled automatically by a speed responsive system including a governor comprising bob weights 18 pivotally mounted on a carrier 19 which is mechanically connected through shaft 20 and gearing 21 with an extension 22 of the engine crankshaft. The governor is thus driven at a function of engine speed. The bob weights 18 act on a movable abutment 23 which is connected to the spindle 24 of a servo control valve 25. Hydraulic liquid under pressure is supplied to the valve by a conduit 26 and conduits 27, 28 are connected to relief. It will be seen that when the valve spindle 24 is moved upwards high pressure liquid is supplied via connection 29 to the upper side of a servo ram piston 30 in a cylinder 31, the lower side of the ram piston being connected via connections 32 to relief. The ram piston 30 is connected via a pivoted link 33 and a link 34 to the butterfly exhaust throttle valve 15.

A spring 35 bears on the upper side of the movable governor abutment 23 and the upper end of this spring is engaged by a further abutment 36 whose position is controlled by a cam 37 connected to a lever 38 so as to be rotated thereby. The lever 38 is connected by a link 39 to the mid-point of a floating link 40, the upper end of this floating link being connected to the manual control lever 8. The lower end of the floating link 40 is connected to a bell crank lever 41 the opposite arm of which is connected to the servo ram piston 30.

In operation therefore the operator will select a power setting by means of the manual control 8 which will adjust the setting of the fuel injection pump control 16 accordingly. At starting and in the lower speed range of the engine the spring 35 overcomes the centrifugal load of the governor bob weights and the valve spindle 24 is held downwards thus admitting servo fluid under pressure to the lower side of the ram piston 30' which will cause the exhaust throttle valve 15 to be moved towards its closed position so as to act as a restriction on the exhaust gases. Since the compressor 11 is of a positive displacement type the pressure of the scavenging and supercharging air admitted to the engine will thus be increased so as to increase the effective output torque of the engine at these lower speeds.

As the engine speed rises the centrifugal effect of the governor bob weights causes the valve spindle 24 to be raised and the servo ram piston 30 will accordingly be moved downwards by the servo pressure, thus opening the throttle valve 15. Any such movement of the ram piston 30 is transmitted through the bell crank lever 41 and links 40, 39 and 38 to the cam 37 which will cause the abutment 36 to be depressed thus re-centering the valve spindle 24 so as to lock the ram piston 30 in its new position. In practice as the engine speed rises the valve 15 will progressively open.

It will be seen that any movement of the manual control 8 to vary the rate of fuel injection and hence the power output-of the engine, will also affect the setting of the cam 37 and the cam will be so designed as to provide the required relationship between the setting of the exhaust throttle valve 15 and the power setting of the lever 8.

What I claim as my invention and desire to secure by Letters Patent is:

A two-stoke engine including an exhaust manifold and an adjustable throttle valve in said exhaust manifold, a positive displacement blower delivering compressed air to the cylinders of the engine, means driving said blower at a speed varying with the speed of the engine, a device directly sensitive to the speed of rotation of the engine, an operative connection between said device and the throttle valve arranged to close the throttle valve progressively as the speed of the engine falls, a fuel setting device on the engine including a manual control therefor, and a connection from the control to the device sensitive to engine speed arranged to adjust the relationship between speed and throttle valve opening at diiferent fuel settings.

References Cited in the file of this patent UNITED STATES PATENTS 2,150,185 Phillips Mar. 14, 1939 2,267,437 Alfaro Dec. 23, 1941 2,423,417 Stokes et al. July 1, 1947 2,444,644 Fullemann July 6, 1948 2,717,583 Maybach Sept. 13, 1955 

